Method and apparatus for preparing monofunctional aromatic chloroformates suitable for use as chainstopping agents

ABSTRACT

The specification describes a continuous process for the preparation of monofunctional aromatic chloroformates (MAC) having the structure (I) 
                         
wherein n is an integer from 1 to 5, and R 1  represents hydrogen, a branched or unbranched alkyl group having from 1–15 carbon atoms, an aryl group which may be substituted or unsubstituted, a cycloaliphatic group which may be substituted or unsubstituted, or an arylalkyl group which may be substituted or unsubstituted.

This application is a Div of Ser. No. 09/281,498 filed Mar. 30, 1999 nowU.S. Pat. No. 6,392,079.

FIELD OF THE INVENTION

This invention relates to a process and apparatus for the continuouspreparation of monofunctional aromatic chloroformate products by aninterfacial process. The monofunctional aromatic chloroformates aresuitable for use as endcapping agents in polymer synthesis.

The present invention further relates to a process for preparation of apolycarbonate, in which the process for continuous preparation ofmonofunctional aromatic chloroformate products is coupled with aninterfacial polycarbonate synthesis. The endcapping agents produced bythe continuous process are introduced into the interfacial polycarbonatesynthesis to obtain the desired polycarbonate product.

The present invention further relates to a method of controlling thevariability of the molecular weight of polycarbonate produced in aseries of batches. The method utilizes the process for the continuouspreparation of monofunctional aromatic chloroformate products by aninterfacial process.

BACKGROUND OF THE INVENTION

The introduction of monofunctional aromatic chloroformates into apolymer synthesis provides a means to control the molecular weight ofthe polymer to be formed. In general, the greater the quantity ofendcapping agent introduced into a polymer synthesis, the lower themolecular weight of the polymer product. Monofunctional aromaticchloroformates are particularly suitable as endcapping agents ininterfacial polycarbonate synthesis because they enable production of apolycarbonate in a single step phosgenation with a substantially lowerlevel of diarycarbonate(s) (DAC) than products produced using ahydroxyaromatic endcap, such as p-cumyl phenol.

Diarylcarbonates have a low melting point, compared with the glasstransition temperature of polycarbonate, and are therefore the lastcomponents to freeze during a polycarbonate molding operation.Therefore, polycarbonate with significant levels of DAC requires longermolding cycle times compared with polycarbonate that is substantiallyfree of DAC. Further, because DAC can sublime, a polycarbonatecontaining diaryl carbonates can lead to undesirable effects, such as“plate out” in which the DAC from previous molding cycles condenses anddeposits on the mold and leads to blemishes in subsequent moldings. Theterm “DAC” as used herein is understood to include also di(alkylphenylcarbonates) and di(arylphenyl)carbonates.

In making monofunctional aromatic chloroformates, it would be desirableto minimize production of by-product DAC. This would enable themonofunctional aromatic chloroformate to be used in a subsequentpolymerization reaction without first being purified by such methods asdistillation. In the following discussion, the term “MAC” or “MACs”refers to a monofunctional aromatic chloroformate compound or mixture ofmonofunctional aromatic chloroformate compounds.

Known process for the production of MACs by an interfacial processinclude the batchwise production of MACs, with subsequent storage forlater use in polymerization.

U.S. Pat. No. 5,399,657 (Van Hout et al) discloses a method of preparingMAC in a batch process. A solution of phosgene in a solvent isintroduced into a reactor, to which phosgene and a phenol compound arethen added while maintaining the temperature at a value in the range of3 to 5° C. The pH is maintained within a desired range by addition of anaqueous caustic solution. Excess phosgene is then depleted from theproduct by reaction with caustic. The production of MACs in U.S. Pat.No. 5,399,657 involve long batch times, typically in the range of 30 to60 minutes.

U.S. Pat. No. 5,274,164 (Wettling et al) discloses a method of preparingaryl chloroformates by the reaction of phenols with phosgene in thepresence of organic phosphorous compounds. The process requires longreaction times, and the addition of a catalyst, such as the organicphosphorous compounds, necessitates extra process steps to recover thecatalyst from the product.

U.S. Pat. No. 4,864,011 (Bussink et al) discloses a method ofpreparation of an aromatic polycarbonate with a MAC endcapping agent.According to Bussink, the MAC is either present prior to phosgeneaddition, or is added at a single point in the batch polymerizationreaction to produce polycarbonate with low DAC. This process, however,has several disadvantages. In order to deliver MAC to the polymerizationreaction at a specific point during the polymerization, the MAC must besynthesized, purified, and stored. Further, delivery of a quantity ofMAC at a specific point in the batch process usually requires anadditional apparatus for storage and charging.

It would be desirable to develop a process whereby the MACs may beproduced directly, without the need for purification, and in acontinuous manner. It would be even more desirable to develop acontinuous process whereby the MACs could be produced in an “on-demand”manner. This would permit direct coupling of the MAC process to a batchor continuous polymerization process, particularly a polycarbonatesynthesis process. Such a directly coupled process would be desirablebecause it would avoid the risks associated with maintaining aninventory of MAC and phosgene-containing materials associated with MACproduction.

An on-demand process for MAC synthesis would further provide asignificant reduction in both phosgene exposure risks and cost ofproduction compared with a batch process for MAC synthesis. None of thedisclosures discussed above meet these criteria.

It would further be desirable to develop a process requiring shorterprocessing times to produce the MACs that may be coupled with acontinuous or batch process for polycarbonate synthesis, respectively(without purification of the MAC) to produce a product having low DACcontent and good quality.

It would also be desirable to develop a process in which excellentmolecular weight control of a polycarbonate produced in an interfacialreaction is achieved. Molecular weight control is usually measured bythe standard deviation of the molecular weight for a series of batches.Good molecular weight control, i.e. control of the variability ofmolecular weight of the polycarbonate produced in a reaction or seriesof reaction, is directly related to control of the molecular weightviscosity. Molecular weight determines molecular weight viscosity;therefore maintaining the molecular weight in a narrow range results inthe maintenance of molecular weight viscosity in a narrow range. It isdesirable to maintain the molecular weight viscosity in a narrow rangeto control processibility of the product. For example, narrow control ofthe molecular weight viscosity over a series of product batches wouldenable a molding machine that is processing polycarbonate from thesebatches to operate for extended periods of time without adjustment.

BRIEF SUMMARY OF THE INVENTION

The present invention solves these problems, and provides furthersurprising properties. These and further objects of the invention willbe more readily appreciated when considering the following disclosureand appended claims.

In a first aspect, the invention relates to a continuous process for thepreparation of monofunctional aromatic chloroformates (MAC) suitable foruse as endcapping agents in polymer synthesis. In one embodiment, theinvention relates to a continuous process for the preparation ofmonofunctional aromatic chloroformate (MAC) having the structure (I)

wherein n is an integer from 1 to 5, and R₁ represents hydrogen, abranched or unbranched alkyl group having from 1–15 carbon atoms, anaryl group which may be substituted or unsubstituted, a cycloaliphaticgroup which may be substituted or unsubstituted, or an arylalkyl groupwhich may be substituted or unsubstituted, the method comprising thesteps of

-   -   a) introducing        -   1) an aqueous caustic solution;        -   2) a carbonyl chloride;        -   3) at least one monofunctional hydroxyaromatic compound; and        -   4) at least one inert organic solvent into a continuous            reaction system; and    -   b) effecting contact between 1), 2), 3) and 4) for a time and at        conditions sufficient to produce a MAC of structure (I).

In another embodiment, the invention relates to a continuous process forthe preparation of an MAC product having the structure (I), as definedabove, comprising the steps of

-   -   a) providing a reaction system comprising a reactor consisting        essentially of a tubular reactor and a means for conveying        fluids through the reactor; the tubular reactor having an input        at the upstream end and an outlet at the downstream end;    -   b) introducing into the tubular reactor at the input of the        upstream end a feed stream comprising an inert organic solvent        and a monofunctional hydroxyaromatic compound;    -   c) introducing into the tubular reactor a carbonyl chloride;    -   d) introducing into the tubular reactor an aqueous caustic        solution;    -   e) effecting contact between the carbonyl chloride, the        monofunctional hydroxyaromatic compound and the aqueous caustic        solution for a time period and at conditions sufficient to yield        the MAC product.

In another embodiment, the invention relates to a tubular reactor systemcomprising

-   -   a) a tubular reactor having an upstream end and a downstream end        and at least one input and at least one output;    -   b) means to introduce carbonyl halide, aqueous caustic solution,        monofunctional hydroxyaromatic compound and inert organic        solvent to the reactor; the carbonyl halide, aqueous caustic        solution, monofunctional hydroxyaromatic compound and inert        organic solvent in the tubular reactor comprising a reaction        mixture;    -   c) means to convey the reaction mixture through the tubular        reactor, under turbulent flow conditions characterized by a        Reynolds number of about 200 to about 100,000.

The invention further relates to MAC prepared by the aforementionedmethods, reaction systems utilizing the method coupled withpolycarbonate polymerization systems, and polycarbonates produced bythese systems.

In a second aspect, the invention relates to a the preparation ofpolycarbonate products in a batch interfacial polymerization processcoupled with the continuous process for the preparation of MAC products,and a method of controlling the variability of molecular weight in aseries of product batches using this process.

In one embodiment, the invention relates method of preparing apolycarbonate comprising the steps of

-   -   a) charging at least one dihydroxy compound, an inert organic        solvent, water, caustic, carbonyl halide, and catalyst to a        vessel, and maintaining the pH of the reaction mixture between        about 4 and about 12; and    -   b) within an interval of between 0 and about 90% of the total        carbonyl halide addition to the vessel, activating a reaction        system that produces monofunctional aromatic chloroformates        (MAC) and introducing the MAC to the vessel within the interval        of 0 to about 90% of the total carbonyl halide addition to the        vessel; where the MAC reaction system is coupled with the        vessel, and where means are provided for delivery of the MAC        from the reaction system to the vessel.

The invention further relates to a method of controlling the variabilityof the molecular weight by repeating the process for the number ofdesired batches, with substantially the same amount of carbonyl halide,caustic and MAC and inert organic solvent.

In a further embodiment, the invention relates to a method of preparinga poylcarbonate comprising the steps of:

-   -   a) charging a vessel with at least one dihydroxy compound, an        inert organic solvent, water, and optionally caustic; thereby        forming a reaction mixture;    -   b) after step a), simultaneously introducing a carbonyl halide        and a caustic to the vessel containing the reaction mixture        while maintaining the pH of the reaction mixture between about 4        and about 12;    -   c) within an interval of between 0 and about 90% of the total        carbonyl halide addition to the vessel, activating a reaction        system that produces monofunctional aromatic chloroformates        (MAC) and introducing the MAC to the vessel within the interval        of 0 to about 90% of the total carbonyl halide addition to the        vessel; where the MAC reaction system is coupled with the        vessel, and where means are provided for delivery of the MAC        from the reaction system to the vessel.

The invention further relates to a method of controlling the variabilityof the molecular by repeating the process for the number of desiredbatches, with substantially the same amount of carbonyl halide, causticand MAC.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of one embodiment of the invention toproduce MAC by a continuous process.

FIG. 2 is a schematic diagram of one embodiment of the invention toproduce polycarbonate, in which a continuous process to product MAC iscoupled with a polycarbonate synthesis reaction.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to thefollowing detailed description of the preferred embodiments of theinvention and the examples included therein.

Before the present method and apparatus are disclosed and described, itis to be understood that this invention is not limited to specificsystemic methods or to particular formulations, as such may, of course,vary. It is also to be understood that the terminology used herein isfor the purpose of describing particular embodiments only and is notintended to be limiting.

In this specification and in the claims which follow, reference will bemade to a number of terms which shall be defined to have the followingmeaning.

The singular forms “a”, “an” and “the” include plural referents unlessthe context clearly dictates otherwise.

“Optional” or “optionally” mean that the subsequently described event orcircumstance may or may not occur, and that the description includesinstances where said event or circumstance occurs and instances where itdoes not.

“Molar flow rate” is in moles per minute, unless otherwise stated.

“Mixture average temperature” is defined as the temperature that amixture of two or more combined streams achieves at equilibrium underadiabatic conditions, i.e., with no input or loss of heat.

An “on-demand” process, as used herein, enables production of therequired amount of product during a specified time interval. Anon-demand process is idle before and after the specified time interval.An on-demand process produces usable product from the moment it isstarted up through the time it is shut down. An on-demand process mayalso be operated continuously over an indefinite time interval, inorder, for example, to feed a continuous polycarbonate synthesis processwith MAC endcap.

A “monofunctional hydroxyaromatic” species, as contemplated herein,contains a single hydroxyl group or hydroxyl radical. In a MAC, thishydroxyl radical is replaced with a chloroformate group.

The term “polycarbonate” as used herein includes copolycarbonates,homopolycarbonates and (co)polyestercarbonates.

The terms “endcapping agent” and “chainstopping agent” are usedinterchangeably.

A “semi-batch” reactor receives an initial charge of materials, afterwhich one or more reactants and optionally solvents are added to thereactor during the course of the reaction. Such reactors, however, areoften referred to simply as “batch” reactors. The terms “batch” and“semi-batch” are used interchangeably throughout the rest of thespecification.

Throughout this application, where publications are referenced, thedisclosures of these publication are hereby incorporated by referenceinto this application in order to more fully describe the state of theart to which this invention pertains.

In one aspect, this invention concerns a continuous process for theproduction of MAC endcapping agents useful in polymer synthesis, inparticular in polycarbonate synthesis.

In another aspect, this invention concerns a process for the productionof polycarbonates in which a process for producing hydroxyaromatichaloformate endcapping agents is coupled with a reaction system forproducing polycarbonate product.

I. Continuous Process for the Production of MACs

As mentioned, in a first aspect, the invention concerns the preparationof MAC products by an continuous process. The MAC products are suitableas endcapping agents in a polymer synthesis. “Reaction system” and“reactor” as used in section (I) of the specification refer to thecontinuous process for the production of MACs suitable for use asendcapping agents, and the equipment used to produce these products.

In semi-batch processes for the production of MAC products, themonofunctional hydroxyaromatic compound feed, a precursor to the MACproduct, may be reacted away as it is fed to the reactor in order tomaintain the concentration of the monofunctional hydroxyaromaticcompound at a low level. In this way, it is possible to minimize the DACformation reaction between the monofunctional hydroxyaromatic compoundand the MAC product.

In contrast, in one embodiment of the continuous process of thisinvention, all of the monofunctional hydroxyaromatic compound is fed toa single input in a plug flow reactor system and reacts as it proceedsthrough the reactor. As the monofunctional hydroxyaromatic compounddisappears by reaction, the MAC concentration increases. Therefore,there is a zone in the plug flow reactor where both the hydroxyaromaticand MAC concentrations are significant. It would be expected that withinthis reactor zone, the production rate of DAC would be rapid and thatthe reactor product would contain a high concentration of DAC. It wasunexpectedly found, however, that the concentration of DAC in theproduct of the continuous process was extremely low, typically in therange of about 300–600 ppm (parts per million), relative to the weightof MAC in the product. This is particularly important for a process formaking MACs that is directly coupled to a polycarbonate synthesisprocess

In a continuous process according to the first aspect of this invention,it was also unexpectedly found that the monofunctional hydroxyaromaticfeed material was virtually fully converted to MAC; only about 0.2 toabout 4 weight percent of unconverted monofunctional hydroxyaromaticfeed remained in the reactor product, relative to the weight of MACproduct.

It was further unexpectedly found that the times for reaction to producethe MAC were very low. Typical reaction times in the batch process toproduce MACs are in the range of about 30 minutes to 60 minutes. In oneembodiment of the present invention, using a tubular reactor, thereaction of hydroxyaromatic compound to chloroformate was complete inabout 1 to 5 seconds.

In batch reaction systems to produce MACs, it is important to maintainrelatively low temperatures in order to avoid high levels of DACformation, for instance, temperatures in the range of below about 10 to15° C. It was unexpectedly found that low DAC product could be obtainedin the continuous reactor system of the invention even when the reactorwas operated adiabatically and allowed to achieve the boilingtemperature of the solvent. In one embodiment, in which the solvent ismethylene chloride, the continuous reaction system may achieve theboiling temperature of the solvent, about 40° C. while producing MACwith low levels of DAC.

More particularly, in a first aspect, the present invention relates to acontinuous process for the interfacial preparation of endcapping agentsuseful in polymer synthesis, the endcapping agents having the formula(I):

where n is an integer from 1 to 5, and R₁ represents hydrogen, abranched or unbranched alkyl group having from 1–15 carbon atoms, anaryl group which may be substituted or unsubstituted, a cycloaliphaticgroup which may be substituted or unsubstituted, or an arylalkyl groupwhich may be substituted or unsubstituted. Endcapping agents produced bythe method of the present invention include, but are not limited to,phenyl chloroformate, t-butyl phenyl chloroformate, p-cumylchloroformate, chroman chloroformate, octyl phenyl or nonyl phenylchloroformate, or a mixture thereof; more preferably phenylchloroformate, p-cumyl chloroformate, or a mixture thereof; even morepreferably p-cumyl phenylchloroformate. Compounds of structure (I) areherein referred to as MACs.

The process of the instant invention is conducted in a reaction systemcomprising a vessel or vessels in which the endcapping agent is producedin continuous manner by interfacial reaction. By “continuous” it ismeant that reactants are introduced and products are withdrawnsimultaneously from the reaction system. Further, the products mayoptionally be withdrawn in their entirety from the moment that thereactor system is started up through the moment that it is shut down,which has the added advantage of supplying MACs “on-demand” to anotherprocess, particularly an interfacial polycarbonate synthesis process.The reaction system may be coupled with a batch polymer synthesis withthe MAC product introduced to the polymer synthesis reactor over a timeinterval, the reaction system may be coupled with a continuous polymersynthesis with the MAC product introduced into the continuous polymersynthesis reactor at a relatively constant rate indefinitely, or the MACproduct may be stored in another vessel for later use.

The reaction system has an upstream inlet or input for introduction offeed and a downstream outlet, for recovery of product. Optionally, theremay be inlets to the reaction system between the upstream inlet and thedownstream outlet for introduction of feed.

The system allows for the continuous production by interfacial reactionof MACs, the product having a low level of DAC and unreactedmonofunctional hydroxyaromatic compound. The continuous process may beconducted in any equipment arrangement in which a continuous reactionmay be effected, including but not limited to a series of continuousstirred tank reactors (CSTRs), a tubular reactor or series of tubularreactors, one or more loop reactors in series and/or parallel, a networkof CSTRs and tubular reactors, a column reactor having mixers in severalstages, and an agitated column. The reaction system may comprise morethan one stage, and cooling as well as introduction of additionalreagents may be effected between stages.

An on-demand process, one embodiment of the invention, must satisfy muchmore rigorous requirements than simple continuous operation. Forexample, for an on-demand MAC synthesis process that is directly coupledto a batch polycarbonate synthesis reactor, the production rate ofbyproducts, e.g. DAC, during MAC synthesis must be low during the entiretime from startup through shutdown. In contrast, many known continuousreaction processes do not have a low byproduct production rate duringstartup, or require lengthy times for startup. For example, chlorinesynthesis is conducted continuously in diaphragm electrolytic cells, butseveral hours are required to start up a chlorine cell, and theby-product hydrogen level is elevated for much of the startup interval.

The continuous process to produce MACs, as described herein, may beoptionally operated as an on-demand process. Alternatively, thecontinuous process of MAC synthesis as disclosed herein may also be usedto produce MACs for storage and subsequent use in, for example, apolycarbonate synthesis. If desired, the MAC may be isolated from thereaction product mixture using well known processes, such asdistillation and decantation. The MAC product may be stored indefinitelyas a solution in a solvent or as a neat liquid. It is preferable to keepthe MAC solution or liquid cool and water-free. If there is any waterpresent in the MAC liquid or solution, the MAC liquid or solution shouldbe acidic.

It should be noted that the invention as disclosed also includesembodiments of continuous processes for MAC production that are noteffective for “on-demand” operation. For example, in one embodiment ofthe invention, a continuous reaction process that comprises a tubularreactor with a short residence time (preferably 0.5 to 30 seconds) isfollowed by a surge tank with a long residence time (preferably greaterthan about 5 minutes). This process for MAC production is continuous butnot on-demand. This process could be coupled to either a continuous or abatch polycarbonate synthesis process and would have the advantagesdescribed herein of MAC synthesis in a short residence time tubularreactor, but would not have the advantage of avoiding an inventory ofMAC and residual phosgene. In contrast, a MAC production reactor thatcomprises a short residence time tubular reactor (without a downstreamsurge tank) that is directly coupled to a polycarbonate synthesisreactor may be operated as either a continuous or an on-demand reactor.

The products of the continuous process for MAC production may be addedto a polycarbonate synthesis prior to or during a batch polycarbonatesynthesis. In one embodiment of the invention, a reaction system inwhich the continuous process for MAC production is effected is coupledwith a batch polymerization reactor, and the products of the MAC reactorare charged to the batch reactor before or during the polycarbonatesynthesis.

The process conditions in the reaction system to produce the MACs may bevaried, and generally any process conditions can be employed providedthat the reaction between the carbonyl chloride and the monofunctionalhydroxyaromatic compound occurs to produce the MAC product. The feedstream or streams entering the reaction system preferably have a mixtureaverage feed temperature in the range of about −10° C. to about 40° C.;more preferably about 0° C. to about 25° C. The feed stream or streamscontain the carbonyl chloride, inert organic solvent, aqueous causticsolution, and monofunctional hydroxyaromatic compound entering thereaction system.

The temperature of the mixture in the reaction system is preferablymaintained below about 60° C., more preferably below about 50° C. Theterm “mixture” as used herein refers to the contents of the reactionsystem, including, but not limited to, the solvent or solvents, thereactants and the caustic. As the reaction is exothermic, thetemperature of the reaction mixture increases as the reaction mixture isconveyed through the reaction system. The temperature at which anyparticular system is maintained depends on the particular solvents,reactants, cooling means, etc.

The reaction system may be cooled or operated adiabatically. Suitablecooling means include a cooling jacket, a pre-cooler heat exchanger, aheat exchanger in a recirculation loop, a heat exchanger betweensections of a multiple reactor system, or a reflux condenser. Thereaction vessel or vessels may be cooled, or heat may be removed betweenthe reaction vessels, if the system comprises more than one stage. Forsimplicity in both design and operation, it is preferable to operate thesystem adiabatically. In order to achieve adiabatic reactor conditions,the reaction vessel or vessels may be insulated according to typicalindustrial practice.

Prior to introduction into the reaction system, the feed stream orstreams may optionally be mixed by suitable mixing means, including butnot limited to, an in-line or static mixer, and an orifice mixer. Asmentioned “feed stream” or “feed streams” as defined herein refers tothe components entering the reaction system, and may include one or morestreams entering the reaction system. A mixing zone may be establishedbefore the reaction system, the reaction system may comprise a mixingzone, or both.

While in the reaction system, the mixture is preferably agitated at anintensity at least sufficient to prevent segregation of the aqueous andorganic phases. If segregation occurs, the conversion of the reactantsto the product will be reduced. The agitation of the aqueous and organicphase should be regulated such that phosgene is not wasted by increasingits hydrolysis rate, which may occur at excessively intense mixing.

In a tubular reactor, one embodiment of the invention, the mixingintensity is often characterized by a tube Reynolds number, defined as:

$N_{Re} = \frac{D\; v\;\rho}{\mu}$

-   -   where D=tube diameter (cm)        -   ν=solution velocity through tube (cm/sec)        -   ρ=solution density (gm/cc)        -   μ=solution viscosity (gm/cm−sec)

It is preferable to maintain the tube Reynolds number in the range ofabout 200 to about 100,000, more preferably in the range of about 200 toabout 20,000.

The mixture in the reaction system may be agitated by mechanical mixingmeans, or alternatively, static mixing elements may be placed in thereaction vessel. Static mixing technology is discussed in “Advances inStatic Mixing Technology”, M. Mutsakis, F. Streiff, and G. Schneider,Chemical Engineering Progress, July, 1986.

The reaction to produce MAC requires an alkali metal base and/or analkaline-earth metal base herein referred to as a caustic compound. Thecaustic compound is preferably introduced as an aqueous caustic solutioncomprising the caustic compound. The aqueous caustic solution preferablycomprises potassium hydroxide, sodium hydroxide and mixtures thereof,even more preferably sodium hydroxide. The aqueous caustic solutionpreferably has a strength of about 10 to about 50 weight percent,preferably between about 15 to about 40 weight percent.

The aqueous caustic solution is preferably introduced into thecontinuous reaction system in a separate stream from the streamcontaining the monofunctional hydroxyaromatic compound and the streamcontaining the carbonyl halide. In one embodiment, the aqueous causticsolution stream is introduced at the upstream input of the reactionsystem. Alternatively, the aqueous caustic solution stream may beintroduced at any point or input in the reaction system which allows thereaction in the system of the carbonyl halide and the monofunctionalhydroxyaromatic compound to form the MAC. The aqueous caustic solutionstream may optionally be split into two or more streams which may havethe same or different molar flow rates. These streams may be introducedat different points in the reaction system. It is preferable tointroduce the aqueous caustic solution stream at the upstream inlet ofthe reaction system.

In one embodiment of the invention, the reaction system furthercomprises a first precooler to establish an input temperature for themonofunctional hydroxyaromatic compound and inert organic solvent, asecond precooler to establish an input temperature for the aqueouscaustic solution, and a mixer that is coupled to the first precooler andthe carbonyl halide feed stream. The monofunctional hydroxyaromaticcompound is preferably dissolved in the solvent in this embodiment. Theaqueous caustic solution is fed to the second precooler. The cooledaqueous caustic solution and the exit stream from the mixer are then fedto the reactor, preferably a tubular reactor.

In the continuous process described herein, it is common for the reactorproduct to contain some unreacted carbonyl chloride and some unreactedcaustic. As caustic is preferably introduced in a separate stream andcaustic is needed for the conversion of the monofunctionalhydroxyaromatic compound to the MAC, it is possible to control theextent of the reaction, or conversion, in a given section of the reactorby adjusting the proportion of caustic solution added to that section.

Under substantially adiabatic reaction conditions, the amount of causticintroduced into the reactor section relative to the amount ofhydroxyaromatic compound and other feed species determines the extent oftemperature increase in that section. The temperature sensitivity of thereaction selectivity towards MAC synthesis and away from DAC formationis a key factor which is considered in determining the amount of causticto be added per stage, the number of stages, and the need for interstagecooling, particularly under adiabatic conditions.

In the present invention, the carbonyl chloride and caustic areintroduced into the reaction system at flow rates which are based onmolar ratios to the monofunctional hydroxyaromatic compound feed rate.Thus, carbonyl halide hydrolysis and the formation of undesired sideproducts, such as DAC, and residual hydroxyaromatic compound areminimized by employing a reaction procedure in which primary attentionis given to maintaining the molar flow ratios of the caustic andcarbonyl halide to the monofunctional hydroxyaromatic compound feedrate, with only secondary attention being directed to pH. These ratiosmay vary depending on the desired quality of the product solution,production rate requirements, and the operating parameters is of thereaction system.

The ratio of the molar flow rates of the carbonyl chloride, such asphosgene, to the monofunctional hydroxyaromatic compound into thereaction system is preferably from about 1.05:1 to about 10:1, morepreferably from about 1.5:1 to about 5:1, even more preferably fromabout 2:1 to about 4:1. The ratio of the molar flow rates of the caustic(as equivalents of NaOH) to the monofunctional hydroxyaromatic compoundin the reaction system is preferably from about 1.1:1 to about 3:1, morepreferably from about 1.2:1 to about 2:1, even more preferably fromabout 1.3:1 to about 1.7:1.

The components may be fed to the reaction system in separate streams, oralternatively, some components may be combined prior to introductioninto the reaction system. For example, the carbonyl chloride and themonofunctional hydroxyaromatic compound may each be introduced in one ormore feed streams, at an input at the upstream end of the reactionsystem or at an input at any point in the reaction system. The overallmolar ratios, however, must be maintained in the reaction system, i.e.between the input and output of the reaction system.

In one embodiment, the carbonyl chloride is mixed with the inert organicsolvent prior to introduction into the reaction system as a homogeneoussolution. In another embodiment, the carbonyl chloride is mixed with theinert organic solvent into which has been dissolved at least onemonofunctional hydroxyaromatic compound, whereupon the mixture is fed asa homogeneous solution. The carbonyl chloride may alternatively beintroduced into the reaction system in the form of a gas. The aqueouscaustic solution is preferably fed to the reaction system in a separatestream from the input stream or streams containing the carbonyl chlorideand the monofunctional hydroxyaromatic compound.

If the reaction system comprises more than one stage, feed may beintroduced into the reaction system between stages. Feed may include oneor more of the following: aqueous caustic solution, inert organicsolvent, carbonyl chloride, and monofunctional hydroxyaromatic compound.In one embodiment, the invention is a tubular reactor which comprisesfrom one to four stages.

The monofunctional hydroxyaromatic compound may be introduced into thereaction system as a solution, as a solid, as a melt, or a mixturethereof. The weight of the monofunctional hydroxyaromatic compound inputto the reaction system, relative to the weight of the inert organicsolvent input to the reaction system is from about 0.5:99.5 to about20:80. The monofunctional hydroxyaromatic compound may be included inwhole or in part in the inert organic solvent stream introduced into thereaction system. In one embodiment, the monofunctional hydroxyaromaticcompound is dissolved in the inert organic solvent and the stream is fedinto an input of the reaction system at the upstream end. If dissolvedin the inert organic solvent, it is preferable that the monofunctionalhydroxyaromatic compound comprises from about 1 to about 20% by weightof the solution. Optionally, carbonyl chloride, such as phosgene, may bedissolved in this stream. Alternatively, the inert organic solvent andthe hydroxyaromatic compound may be introduced in separate streams atthe input of the reaction system at the upstream end, or each stream maybe divided into two or more streams and introduced at input points alongthe reaction system.

The residence time of the reaction mixture in the reaction system is afunction of volumetric flow rate through the reaction system. If thereaction system is a tubular reactor, for instance, the length anddiameter of the reactor may be varied to achieve a desired residencetime and thereby achieve an optimum yield of the desired MAC product.

Design consideration that are common to plug flow reactors are describedby Levenspiel in Chemical Reaction Engineering, John Wiley and Sons,1962. Preferably, the length to diameter ratio of the tubular reactor isat least about 10, and more preferably at least about 20.

In the present invention it was surprisingly found that the residencetime in the reactor is not critical. It was also surprisingly found thatextra residence time in the reactor will not degrade the product. Ingeneral, the reaction occurs at a fast rate; the preferred residencetime in the reactor may vary from about 0.5 seconds to about 30 secondsper stage, more preferably from about 1 to about 10 seconds per stage.

It is preferable to maintain the reaction system at substantially aminefree conditions. By “substantially amine free” it is meant that the flowrate weighted average of the amine levels, including but not limited totriethylamines, in all feed streams be maintained at less than 50 partsper million (ppm), preferably below about 10 ppm, even more preferablybelow about 5 ppm. The presence of amines in the reaction system leadsto undesirable side products, such as DAC. Optionally the feed stream(s)entering the reaction system may be purified by acid extraction; any ofthe feed streams may be purified by passing the desired stream over anadsorbent bed to remove free amines. In addition, it is also preferableto avoid other condensation catalysts besides amines, including but notlimited to quaternary ammonium salts and quaternary phosphonium salts,and organo-phosphorous catalysts

Optionally, the MAC reaction product may be treated with furtherprocessing steps. Although the MAC reaction product from the process ofthis invention has sufficiently low DAC levels to be used withoutfurther purification for polymer production, such as a polycarbonate,optionally, the product solution may be further purified by fractionaldistillation prior to introduction into a polymerization, i.e. apolycarbonate synthesis.

In one embodiment, the process of the instant invention is conducted ina tubular reactor system as illustrated in FIG. 1. The tubular reactormay be situated in any manner; however it is preferred that the tubularreactor is horizontally displaced. Feed stream 1, containingmonofunctional hydroxyaromatic compound and solvent are fed to precooler3. The product of precooler 3 and feed stream 2 containing carbonylchloride, such as phosgene, are fed to mixer 4. A separate stream of anaqueous caustic solution 5 is fed into precooler 6. The effluents frommixer 4 and precooler 6 are then fed into the tubular reactor 7. Thediagram of reactor 7 includes mixing elements in the reactor.Optionally, tubular reactor 7 may be insulated. The effluent fromtubular reactor 7, containing the MAC product (product stream) may befurther processed, or it may be directed into a polymer synthesisreactor, for example a polycarbonate synthesis reactor.

The process as shown in FIG. 1 may be operated continuously or in anon-demand manner, depending on the intended use of the MAC product. Ifthe process is operated in an on-demand manner, it may be started whilea batch polycarbonate synthesis is being conducted in a separate vessel.The MAC product may be introduced into the polycarbonate synthesisreactor during the phosgenation step of the batch polycarbonatesynthesis, and then stopped prior to completion of the polycarbonatebatch. The MAC product stream may be delivered directly into thepolycarbonate synthesis reactor without the need for furtherpurification.

As shown in FIG. 2, a tubular reactor system may be connected in seriesto a polycarbonate synthesis reactor 17. One embodiment of the batchpolymerization is discussed in section II of the specification. Thepolycarbonate synthesis reactor may be operated either continuously orin a batch mode. In the continuous operating mode, the product from thereactor 7 is continuously introduced into the polycarbonate synthesisreactor 17. In a batch operating mode, the polycarbonate reactor may becharged with monomer, for example bisphenol-A (BPA) 11, solvent 12,catalyst 13, water 14, phosgene 15, and an aqueous caustic solution 16as disclosed in U.S. Pat. No. 4,864,011, incorporated herein byreference. In the polymerization disclosed in U.S. Pat. No. 4,864,011, aMAC chainstopper is added to the polycarbonate synthesis reaction after20 to 80 percent of the carbonyl halide that is to be added in total hasbeen supplied to the reactor. Each example in U.S. Pat. No. 4,864,011shows the entire charge of chloroformate being added at a single pointin the batch polymerization process.

The following discussion sets forth the reactants, including caustic,and solvents which are suitable for use in the preparation of the MACproducts suitable for use as endcapping agents. The particularcomponents described are for illustrative purposes only, and theprovided lists are not intended to be exhaustive.

Suitable monofunctional hydroxyaromatic compounds which may be used inthe process of the present invention to prepare MAC are represented bythe general formula (II):

where n is an integer from 1 to 5, and wherein R₁ represents hydrogen, abranched or unbranched alkyl group having from 1–15 carbon atoms, anaryl group which may be substituted or unsubstituted, a cycloaliphaticgroup which may be substituted or unsubstituted, or an arylalkyl groupwhich may be substituted or unsubstituted. It is preferred that n isequal to 1 and that R₁ is present in the para position.

Monofunctional hydroxyaromatic compounds as defined in formula (II)include, but are not limited to, phenol, p-tert-butylphenol, o-cresol,m-cresol, p-cresol, o-ethylphenol, p-ethylphenol, p-cumylphenol,chroman, p-octylphenol, p-nonylphenol, α-napthol, β-napthol and mixturesthereof. Preferred monofunctional hydroxyaromatic compounds are phenol,t-butyl phenol, p-cumyl phenol, chroman, and mixtures thereof; p-cumylphenol is more preferred.

Suitable carbonyl halides for use in the present process, include, butare not limited to carbonyl chlorides, such as phosgene, carbonylbromide, carbonyl iodide, carbonyl fluoride and mixtures thereof. Othercarbonyl chlorides including diphosgene and triphosgene are alsosuitable. Phosgene is the preferred carbonyl halide. The carbonyl halidemay be introduced into the reaction system in the form of a gas or aliquid, or it may be dissolved in any feed stream except the causticfeed stream before the introduction of the feed stream into the reactionsystem. It is therefore possible to prepare other haloformates, such asbromoformates, etc. by the process of the invention. Chloroformates arethe most preferred.

Suitable inert organic solvents for use in the process of the presentinvention include any inert organic solvent which is substantiallyinsoluble in water and inert to the process conditions. The inertorganic solvent should also be a liquid under the reaction conditionsand should not react with the carbonyl halide, the hydroxyaromaticcompound or the caustic. It is desirable that the MAC product be solublein the solvent. Suitable inert organic solvents include, but are notlimited to aliphatic hydrocarbons such as pentane, hexane, cyclohexane,and heptane; aromatic hydrocarbons such as toluene, xylene; substitutedaromatic hydrocarbons, such as chlorobenzene, dichlorobenzene, andnitrobenezene; chlorinated aliphatic hydrocarbons such as chloroform andmethylene chloride, and mixtures of any of the aforementioned solvents.The aforementioned solvents may also be mixed with ethers, including butnot limited to tetrahydrofuran. Chlorinated aliphatic hydrocarbons arepreferred, in particular methylene chloride.

The reaction to produce the MAC requires an alkali metal base and/or analkaline-earth metal base, herein referred to as a caustic. The causticcompound is preferably introduced as an aqueous solution comprising thealkali metal base and/or alkaline-earth metal base.

Suitable alkali metal compounds which may be used as a caustic in thereaction system include, but are not limited to, sodium hydroxide,potassium hydroxide, lithium hydroxide, sodium hydrogen carbonate,potassium hydrogen carbonate, lithium hydrogen carbonate, sodiumcarbonate, potassium carbonate, lithium carbonate and mixtures thereof.

Suitable alkaline-earth metal compounds which may be used as a causticin the reaction system include, but are not limited to, calciumhydroxide, barium hydroxide, magnesium hydroxide, strontium hydroxide,calcium hydrogen carbonate, barium hydrogen carbonate, magnesiumhydrogen carbonate, strontium hydrogen carbonate, calcium carbonate,barium carbonate, magnesium carbonate, strontium carbonate and mixturesthereof.

The strength of the aqueous caustic solution may be varied, however itis preferable that the caustic compound comprise from about 10 wt % toabout 50 wt % of the aqueous caustic solution, preferably between about15 to about 40 wt %. The most preferred caustic is sodium hydroxide, andthe aqueous caustic solution preferably comprises from about 15 wt % toabout 40 wt % sodium hydroxide.

II. Batch Process for the Production of Polycarbonate by InterfacialPolymerization

In a second aspect, the present invention concerns the preparation ofpolycarbonate products in a batch interfacial polymerization processcoupled with the continuous process for the preparation of MAC productsas set forth in section I of the specification, and a method ofcontrolling the variability of molecular weight in a series of productbatches using this process.

Polycarbonates which may be prepared by the method of this inventiontypically comprise structural units of the formula

wherein at least about 60% of the total number of R groups are aromaticorganic radicals and the balance thereof are aliphatic, alicyclic oraromatic radicals. Preferably, each R is an aromatic organic radical andmore preferably a radical of the formula

wherein each A₁ and A₂ is a is a monocyclic divalent aryl radical and Yis a bridging radical in which one or two carbonate atoms separate A₁and A₂. Such radicals may be derived from dihydroxyaromatic compounds ofthe formulas OH—R—OH and OH-A₁-Y-A₂-OH, or their correspondingderivatives. A₁ and A₂ include but are not limited to unsubstitutedphenylene, preferably p-phenylene or substituted derivatives thereof.The bridging radical Y is most often a hydrocarbon group and preferablya saturated group, such as methylene, cyclohexylidene or isopropylidene.Isopropylidene is the more preferred. Thus, the more preferredpolycarbonates are those comprising residues of2,2-bis(4-hydroxyphenyl)propane, also known as “bisphenol A”. In oneembodiment, the polycarbonate is a homopolymer of bisphenol A.

(Co)polyestercarbonates may also be prepared by the method of thisinvention. The polyestercarbonate may comprise residues of aliphatic oraromatic diacids. The corresponding derivatives of aliphatic or aromaticdiacids, such as the corresponding dichlorides, may also be utilized inthe polymerization.

Polyfunctional compounds may also be introduced into the reaction toproduce, for example, branched polycarbonates.

Polycarbonates, including aromatic polycarbonates, are typicallyproduced interfacially by the reaction of a carbonyl halide, such asphosgene, and a bisphenol, such as bisphenol A, in the presence of aphenolic endcapping agent. Known methods include the addition of thephenolic endcapping agent at the beginning of the interfacial reactionwhich leads to the production of undesirable diarylcarbonates (DAC). Incontrast, in a preferred batch polycarbonate synthesis process asdescribed herein, the MAC is prepared in an on-demand manner and addedover a finite interval during the batch polymerization.

It was unexpectedly found that when the batch polymerization reaction toproduce polycarbonates, as defined in section II of the specification,was coupled with the continuous process for the production of MAC asdescribed in section I of the specification, the molecular weight of thepolycarbonate product over a series of batches showed less variabilitythan when previously known methods for endcap addition, such as theaddition of molten or solid endcap, in particular p-cumyl phenol, wereused

It was also unexpectedly discovered that, when the batch polymerizationreaction to produce polycarbonate was coupled with the continuousprocess for the production of MAC as set forth in Section I of thespecification, by adding the MAC endcap over an interval during thebatch polycarbonate synthesis, that the final DAC level in thepolycarbonate product was lower than the level previously obtained byadding MAC to the polycarbonate synthesis at a single point in the batchpolycarbonate synthesis process, as was disclosed by Bussink et al inU.S. Pat. No. 4,864,011.

In one embodiment, the combined MAC and batch polycarbonate synthesiscomprises the steps of

-   -   1) charging at least one dihydroxy compound, an inert organic        solvent, water, caustic, carbonyl halide, and catalyst to a        vessel, and maintaining the pH of the reaction mixture between        about 4 and about 12 during charging; and    -   2) within an interval of between 0 and about 90% of the total        carbonyl halide addition to the vessel, activating a reaction        system that produces monofunctional aromatic chloroformates        (MAC) and introducing the MAC to the vessel within the interval        of 0 to about 90% of the total carbonyl halide addition to the        vessel; where the MAC reaction system is coupled with the        vessel, and where means are provided for delivery of the MAC        from the reaction system to the vessel.

In a further embodiment, the combined MAC and batch polycarbonateprocess of this invention preferably comprises the steps of

-   -   1) charging a batch polymerization reactor with at least one        dihydroxy compound, solvent, and water, and optionally caustic    -   2) simultaneously charging carbonyl halide and caustic to the        reactor, while maintaining a pH of the reaction in a specified        range,    -   3) charging the batch polymerization reactor with the MAC        reactor products during a specified interval of the batch        polymerization process, and    -   4) recovering the polycarbonate polymer from the batch        polymerization reactor.

The first step of the process is referred to herein as the batchformulation. In this step, a batch interfacial polycarbonate reaction isgenerally initiated by charging a vessel with a mixture of solvent, oneor more monomers, for example bisphenol A, and optionally a comonomersuch as 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane), water, andcatalyst, such as triethylamine. The relative amounts of solvent andmonomer are established in order to achieve a desired finalpolycarbonate concentration in the organic phase preferably in the rangeof from about 5 wt % to about 25 wt %, more preferably in the range offrom about 15 wt % to about 25 wt %, accounting for solvent added duringthe formulation as well as solvent added during the MAC synthesis andaddition. The amount of water added during the batch formulation isestablished so that the final concentration of byproduct alkali halide,for example sodium chloride, is preferably in the range of from about 10wt % to saturation, which is about 26 wt % for sodium chloride, and morepreferably from about 15 wt % to about 25 wt %. These ranges arecommonly used in industry and are described in U.S. Pat. No. 3,173,891,herein incorporated by reference.

During the batch phosgenation of the polycarbonate reaction, alkalimetal base and/or alkaline earth metal base is added to maintain thereaction pH preferably in the range of about 4 to about 12, morepreferably in the range of about 7 to about 11 for polyester carbonatereactions, and more preferably in the range of about 9 to about 11 forBisphenol A polycarbonate synthesis reactions. The types andconcentrations of bases described in Section I of the specification arealso usable in the polycarbonate synthesis process.

During the batch formulation, the MAC synthesis reactor is idle, if theMAC synthesis reactor is operated as an on-demand process. It ispreferable to operate the reaction system as an on demand process. TheMAC synthesis reactor may start either at or about the time phosgeneaddition begins or at a specified time after the carbonyl halide, suchas phosgene addition starts for the batch polymerization reactor. When apredetermined condition in the batch polymerization has been achieved,for example, a specific percent of the total carbonyl halide addition,the MAC synthesis reactor is started and the MAC reactor products aredelivered to the batch polymerization reaction over a predeterminedinterval. Again, this interval is usually specified in terms of apercentage of the total carbonyl halide target to the polymerizationreactor.

Preferably, the MAC product mixture prepared by the on demand process isadded during the interval of 0 and about 90 percent of the phosgeneaddition to the batch polycarbonate synthesis. More preferably, the MACproduct mixture from the on demand process is added during the intervalof about 10 and about 80 percent of the phosgene addition to the batchpolycarbonate synthesis. Even more preferably, the MAC product mixturefrom the on-demand process is added during the interval of 10 and about60 percent of the phosgene addition to the batch polycarbonatesynthesis. Alternatively, if the MAC synthesis process is simplycontinuous, and not on demand, the batch polymerization reactor may befed with MAC product mixture over the same intervals noted above, butthe MAC product mixture is fed from a storage vessel, such as a surgetank, rather than directly from the MAC synthesis reactor.

The carbonyl halide and caustic addition rates for the polycarbonatesynthesis reaction may vary during the course of the polymerizationreaction. Although it is preferable to add both the phosgene and causticto the polymerization reaction during the interval that MAC is beinggenerated and added to the polymerization reactor in order to minimizethe batch reaction cycle time, it is within the scope of this inventionto suspend or reduce phosgene and/or caustic addition to thepolymerization reactor during part or all of the interval during whichMAC is fed to the polymerization reactor.

The total amount of MAC added to the batch polycarbonate synthesis is inthe range of about 1 mole percent to about 20 mole percent, based on thenumber of moles of difunctional monomer in the polymerization, andpreferably in the range of about 1 mole percent to about 7 mole percent,based on the number of moles of difunctional monomer in thepolymerization. The rate of addition of the MAC product mixture to thepolycarbonate synthesis may vary over the course of addition to thebatch polymerization reaction, but it is preferable to add the MACmixture at a substantially constant rate to the polycarbonate synthesis.

It is preferable to predetermine a reaction endpoint for the batchinterfacial polycarbonate synthesis reaction. The predetermined reactionendpoint for a batch interfacial polycarbonate synthesis reaction maybe, for example, attainment of a specific total amount of phosgene orcaustic addition to the polycarbonate synthesis reaction. Alternatively,the properties of the reactor contents may be measured intermittently orcontinuously, for example the weight average molecular weight may bemonitored by laser light scattering. When the measured property achievesa desired level, this signifies the reaction endpoint. At this point,the carbonyl halide addition is stopped; caustic addition may continueuntil a final reaction pH is achieved.

The polycarbonate from the batch polymerization process may be recoveredaccording to practices well known in the art for solutionpolymerizations. Several well-known techniques such as antisolventprecipitation are described in Chemistry and Physics of Polycarbonates,H. Schnell and Polycarbonates, by W. F. Christopher and D. W. Fox.

The transport of the MAC from the continuous reaction system used toproduce the MAC to the polycarbonate synthesis reaction (batchpolymerization reaction) may be accomplished by any suitable deliverysystem, for example, a pipe between the two reaction systems. Thedelivery time between the MAC reaction system and the polycarbonatesynthesis depends on the length and diameter of the delivery system; itis preferable that the delivery time is in the range of about 1 to about30 seconds. Preferably, the MAC reaction system is placed as close aspossible to the batch reactor to minimize the potential of phosgeneexposure risk.

It should be noted that the MAC purity is unaffected by delays inadditional piping between the MAC synthesis reactor and thepolycarbonate synthesis reactor. The reaction product from thecontinuous process for the production of MAC as described in section Iof the specification contains not only MAC, but also unreacted carbonylhalide and caustic, as well as solvent and aqueous alkali halidesolution. Therefore, if any hydrolysis of the MAC product back tomonofunctional hydroxyaromatic compound occurs within the tubularreactor or while the MAC product mixture is being conducted to thepolycarbonate polymerization reactor, the residual carbonyl halide andcaustic will tend to reconvert hydrolyzed product to the desired MAC.

The following discussion sets forth reactants and solvents which aresuitable for use in the preparation of the polycarbonates by a batch orcontinuous interfacial polymerization process. The solvents, caustic,carbonyl halides, and monofunctional hydroxyaromatic compounds which maybe used in the production of the MAC as discussed in section (I) of thespecification may also be used in the batch process for the preparationof polycarbonate. The particular reactants and catalysts as describedare for illustrative purposes only, and the provided lists are notintended to be exhaustive.

Suitable carbonyl halides for use in the polycarbonate synthesisprocess, include, but are not limited to carbonyl chloride, carbonylbromide, carbonyl iodide, carbonyl fluoride and mixtures thereof.Diphosgene and triphosgene are also suitable carbonyl halides. Phosgeneis the preferred carbonyl halide.

It is to be understood that, although “chloroformates” are the preferredendcapping agent produced and utilized according to the method of thisinvention as described in sections I and II of the specification, otherhaloformates may be prepared, and have the general formula described informula V, below, in which X represents fluorine, bromine, chlorine oriodine. The corresponding carbonyl halide, as discussed above would beutilized in production of the haloformate endcapping agent.

Suitable organic solvents for use in the polycarbonate synthesis includeany organic solvent which is substantially insoluble in water and inertto the process conditions. The organic solvent should also be a liquidunder the reaction conditions and should not react with the carbonylhalide, or the caustic. Suitable organic solvents include, but are notlimited to aliphatic hydrocarbons such as pentane, hexane, cyclohexane,and heptane; aromatic hydrocarbons such as toluene, xylene; substitutedaromatic hydrocarbons, such as chlorobenzene, dichlorobenzene, andnitrobenezene; chlorinated aliphatic hydrocarbons such as chloroform andmethylene chloride, and mixtures of any of the aforementioned solvents.The aforementioned solvents may also be mixed with ethers, including butnot limited to tetrahydrofuran. Chlorinated aliphatic hydrocarbons arepreferred, in particular methylene chloride.

Suitable bisphenols or diphenols which may be used in the polymerizationof polycarbonate include, but are not limited to,

-   resorcinol,-   4-bromoresourcinol,-   hydroquinone,-   4,4′-dihydroxybiphenyl,-   1,6-dihydroxynapthalene,-   bis(4-hydroxyphenyl)methane,-   bis(4-hydroxyphenyl)diphenylmethane,-   bis(4-hydroxyphenyl)-1-napthylmethane,-   1,1-bis(4-hydroxyphenyl)ethane,-   1,2-bis(4-hydroxyphenyl)ethane,-   1,1-bis(4-hydroxyphenyl)phenylethane,-   2,2-bis(4-hydroxyphenyl)propane (“bisphenol A”),-   2-(4-hydroxyphenyl)-2-)3-hydroxyphenyl)propane,-   2,2-bis(4-hydroxyphenyl)butane,-   1,1-bis(4-hydroxyphenyl)isobutane,-   1,1-bis(4-hydroxyphenyl)cyclohexane,-   trans-2,3-bis(4-hydroxyphenyl)-2-butene,-   2,2-bis(4-hydroxyphenyl)adamantane,-   α,α′-bis(4-hydroxyphenyl)toluene,-   bis(4-hydroxyphenyl)acetonitrile,-   2,2-bis(3-methyl-4-hydroxyphenyl)propane,-   2,2-bis(3-ethyl-4-hydroxyphenyl)propane,-   2,2-bis(3-n-propyl-4-hydroxyphenyl)propane,-   2,2-bis(3-sec-butyl-4-hydroxyphenyl)propane,-   2,2-bis(3-t-butyl-4-hydroxyphenyl)propane,-   2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane,-   2,2-bis(3-allyl-4-hydroxyphenyl)propane,-   2,2-bis(3-methoxy-4-hydroxyphenyl)propane,-   2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane,-   2,2-bis(2,3,5,6-tetramethyl-4-hydroxyphenyl)propane,-   2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane,-   2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane,-   2,2-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)propane,-   α,α-bis(4-hydroxyphenyl)toluene,-   α,α,α′,α′-tetramethyl-α,α′-bis(4-hydroxyphenyl)p-xylene,-   2,2-bis(4-hydroxyphenyl)hexafluoropropane,-   1,1-dichloro-2,2-bis(4-hydroxyphenyl)ethylene,-   1,1-dibromo-2,2-bis(4-hydroxyphenyl)ethylene,-   1,1-dichloro-2,2-bis(5-phenoxy-4-hydroxyphenyl)ethylene,-   4,4′-dihydroxybenzophenone,-   3,3-bis(4-hydroxyphenyl)-2-butanone,-   1,6-bis(4-hydroxyphenyl)-1,6-hexanedione,-   ethylene glycol bis(4-hydroxyphenyl)ether,-   bis(4-hydroxyphenyl)ether,-   bis(4-hydroxyphenyl)sulfide,-   bis(4-hydroxyphenyl)sulfoxide,-   bis(4-hydroxyphenyl)sulfone,-   bis(3,5-dimethyl-4-hydroxyphenyl)sulfone,-   9,9-bis(4-hydroxyphenyl)fluorene,-   2,7-dihydroxypyrene,-   6,6′-dihydroxy-3,3,3′,3′-tetramethylspiro(bis)indane-   (“spirobiindane bisphenol”),-   3,3-bis(4-hydroxyphenyl)phthalide,-   2,6-dihydroxydibenzo-p-dioxin,-   2,6-dihydroxythianthrene,-   2,7-dihydroxyphenoxathiin,-   2,7-dihydroxy-9,10-methylphenazine,-   3,6-dihydroxydibenzofuran,-   3,6-dihydroxydibenzothiophene,-   2,7-dihydroxycarbazole,-   4,4-bis(4-hydroxyphenyl)heptane,-   2,2-bis(4-hydroxyphenyl)hexane,

and other halogenated or alkylated derivatives. It is also possible touse mixtures of mono- and/or bischloroformates of the desired bisphenolor mono- and/or bischloroformate oligomeric carbonate mixtures of thedesired bisphenol. 2,2-bis(4-hydroxyphenyl)propane (or bisphenol A) isthe preferable bisphenol. The corresponding derivates of the diphenolsmay also be used.

Suitable polyfunctional compounds used in the polymerization of branchedpolycarbonate include, but are not limited to,

-   1,1,1-tris(4-hydroxyphenyl)ethane,-   4-[4-[1,1-bis(4-hydroxyphenyl)-ethyl]-dimethylbennzyl],-   trimellitic anhydride,-   trimellitic acid, or their acid chloride derivatives.

Suitable dicarboxylic acids or dicarboxylic dichlorides which may beused with bisphenols in the polymerization of polyester carbonatesinclude, but are not limited to,

-   1,10-decane dicarboxylic acid,-   1,12-dodecane dicarboxylic acid,-   terephthalic acid,-   isophthalic acid,-   terephthaloyl dichloride, and isophthaloyl dichloride.

The polycarbonate synthesis may be conducted in the presence of acatalyst, for example a tertiary amine and/or a phase transfer catalyst,such as a tetraalkylammonium salt. Suitable tertiary amine catalystsinclude, but are not limited to triethylamine, tripropylamine, andtributylamine. Phase transfer catalysts include but are not limited totetrabutylammonium bromide and methyl tributylammonium bromide. Theamine catalyst level may be in the range of from about 0.25 to about 10mole percent based on dihydroxy compound. The phase transfer catalystmay be in the range of zero to about 2 mole percent based on thedihydroxy compound. The catalyst mixture may be charged to the reactorprior to addition of the carbonyl halide addition or may be programmedinto the batch or continuous polymerization reactor during addition ofthe carbonyl halide.

EXAMPLES

The following examples are set forth to provide those of ordinary skillin the are with a complete description of how the compositions of matterand methods claimed herein are made and evaluated, and are not intendedto limit the scope of what the inventors regard as their invention.Efforts have been made to insure accuracy with respect to numbers (e.g.,amounts, temperature, etc.) but some errors and deviations should beaccounted for. Unless indicated otherwise, parts are by weight,temperature is in ° C.

Example 1

A tubular reactor was constructed of 0.25 inch outer diameter 316stainless steel tubing and SWAGELOK® fittings, manufactured by SwagelokCompany, and was packed with static mixing elements. The overall lengthof the reactor was 16.5 inches. The reactor was insulated with wovenfabric insulating material. The reactor was fed from two feedstreams: asolution of phosgene and p-Cumyl Phenol (PCP) in methylene chloride, andNaOH/water. Each feed solution was pumped independently to the reactorvia a pre-cooling coil immersed in a water bath that was held at 4° C.The details of the reaction are shown in the table below. The productcomposition is reported as parts by weight of the organic phase product.

For Examplewt % PCP=100(wt PCP)/(wt PCP+wt PCF+wt DAC)

Feed (1): 4.5 gm/min p-cumyl phenol 92.1 gm/min methylene chloride 4.2gm/min COCl₂ Feed (2): 25 wt % NaOH Solution

mole NaOH/mole Product DAC Product PCP Expt PCP (ppm) (wt %) A 1.0 6330.46–3.32 B 1.2 421 0.248 C 1.5 336 0.228

The balance of the aromatic product of these reactions was p-cumylphenyl chloroformate, the desired product. These results show that verylow levels of DAC and essentially complete PCP conversion are achievedwith the process of this invention.

Example 2

A tubular reactor was constructed as in example 1 except that itcomprised two 7 inch sections that contained mixing elements followed bya 50 foot section of unpacked tubing. The entire reactor was insulatedwith woven fabric. This reactor was fed with feeds 1 and 2 as shownbelow. The feeds were cooled to 4° C. prior to being introduced into thereactor. The reaction was sampled after the first and second 7 inchmixing section and after the 50 foot unpacked section.

Feed (1): 4.5 gm/min p-cumyl phenol 92.1 gm/min methylene chloride 4.2gm/min COCl₂ Feed (2): 25 wt % NaOH Solution (1.5 mole NaOH/mole PCP)

The product composition is shown below. The balance of the aromaticproduct was p-cumyl phenyl chloroformate.

Sample Point ppm DAC wt % PCP 7″ 430 0.7 14″ 410 1.2 14″ + 50 Feet 4300.6

This example shows that the product is not further converted to DAC uponadditional residence time in the tubular reactor or in downstreampiping.

Example 3

Example 2 was repeated with 5 ppm triethylamine in the methylenechloride feed solution. The results are given in the table below.

Sample Point ppm DAC wt % PCP 7″ 530 0.7 14″ — 0.6 14″ + 50 Feet 600 0.5

This shows that the reaction product is sensitive to the presence of lowlevels of triethylamine.

Example 4

Example 2 was repeated using only the two packed sections and with thefollowing feed composition. The precooling bath temperature was adjustedto values between 20 and 35° C. The product composition was measured atthe end of the second mixing zone.

Feed (1): 4.5 gm/min p-cumyl phenol 92.1 gm/min methylene chloride 5.2gm/min COCl₂ Feed (2): 24 wt % NaOH Solution (1.5 mole NaOH/mole PCP)

Bath Temp C. ppm DAC wt % PCP 20 325 0.7 25 420 0.5 30 460 0.8 35 4700.6

This example shows that the reaction may be run over a wide range oftemperature without introducing high levels of DAC in the product.

EXAMPLES (POLYCARBONATE)

The following examples relate to the preparation of a polycarbonate by abatch interfacial polymerization process coupled with the continuousprocess for the preparation of MAC, used as an endcapping agent.

Examples 5–10

A chloroformate synthesis reactor was constructed of TEFLON lined pipeand packed with static mixing elements. The reactor was 1 inch insidediameter by 5 feet in length. The reactor was fed with threefeedstreams: a solution 4 wt % p-cumylphenol (PCP) in methylenechloride, phosgene gas, and a 25 wt % solution of NaOH in water. The PCPsolution was pumped through a heat exchanger to the cool it to thedesired feed temperature before sending it to the chloroformatesynthesis reactor.

An agitated polycarbonate synthesis reactor was equipped with inlets tocharge phosgene and NaOH, a pH probe to measure and control the pH ofthe reaction, and a reflux condenser. This reactor was charged with BPA(200 pounds), water (56 gallons), methylene chloride (93 gallons) andtriethlyamine (450 ml). Phosgene (250 pounds/hour) was added to thepolycarbonate synthesis reactor and an aqueous caustic solution (50 wt %NaOH) was added to maintain a pH of 9–11. While maintaining the phosgeneand NaOH flows to the polycarbonate reactor, the MAC synthesis reactorwas flushed with methylene chloride into the polycarbonate reactor.Phosgene and NaOH/water where then added to the methylene chloride flushat predetermined rates described in the table below. After the flows ofthe phosgene and NaOH/water were established, the methylene chlorideflush was stopped and a cooled solution of 4 wt % PCP in methylenechloride (257 pounds) was pumped to the chloroformate synthesis reactorwhile maintaining the phosgene and NaOH/water flows to the chloroformatesynthesis reactor. After the addition of the 4 wt % PCP methylenechloride, the chloroformate synthesis reactor was flushed briefly withmethylene chloride and the flows of phosgene and NaOH/water werestopped. The phosgene flow was continued to the polycarbonate reactoruntil a total of 87 pounds was achieved. During this time, the pH wasmaintained at 9–11 by addition of 50% NaOH. After the phosgene was shutoff, the methylene chloride phase of the polycarbonate reaction wassampled. The resulting polymer analyzed for di-p-cumylphenylcarbonate (aDAC) and the results are reported below.

The following definitions are used in the table below.

-   Start Time=Time in minutes after the start of phosgenation when the    MAC reactor was started.-   Feed Time=Time interval during which the 4 wt % PCP in methylene    chloride solution is fed to the chloroformate synthesis reactor.-   wt % NaOH=The weight percent NaOH in water added to the MAC    synthesis reactor.-   R_(NaOH)=Mole of NaOH per mole of PCP fed to chloroformate synthesis    reactor-   R_(phos)=Mole of phosgene per mole of PCP fed to chloroformate    synthesis reactor

Start Feed Feed ppm EX time Time Temp wt % NaOH R_(NaOH) R_(phos) DAC 54 7 55 20 1.5 3.5 174 6 4 5 45 25 1.5 2.8 74 7 2 5 55 25 1.5 2.8 82 8 27 55 30 1.5 3.5 102 9 4 5 55 30 1.5 2.8 75 10 2 5 55 0 0 0 2100

The above table shows that the polymer product DAC level is below about200 ppm over a broad range of MAC synthesis reactor operatingconditions. For comparison, Example 10 shows that the polymer productDAC level was significantly higher when neither phosgene nor causticwere added to the chloroformate synthesis reactor. This represents thepolymer product DAC level that occurs when PCP rather than p-cumylphenyl chloroformate is added to the polycarbonate synthesis reactorover an interval during polycarbonate synthesis.

Example 11 (Polycarbonate)

The combined chloroformate synthesis reactor and polycarbonate synthesisreactor were operated as in Example 5 (POLYCARBONATE) to make a seriesof six polycarbonate batches with the same MAC endcap level. The productweight average molecular weight (M_(w)) was measured for each batch. Wewere surprised to find that the molecular weight was quite consistent,as shown in the table below. For this data set, the standard deviationof the molecular weight is only 52 Mw units, which is comparable to thevariability of the molecular weight measurement. When the conventionalendcap addition technique is used, the molecular weight variability isabout 150 Mw units.

Batch DAC ppm Mw a 220 17,600 b 150 17,620 c 220 17,600 d 180 17,575 e125 17,500 f 180 17,500

Comparative Example 1

Bussink et al (U.S. Pat. No. 4,864,011) report DAC levels forpolycarbonate polymerizations in which all the MAC was added at a singlepoint in the phosgenation reaction. The MAC (as phenyl chloroformate)endcap level for the reactions reported by Bussink was 5.6 mole percentof the BPA repeat units. In the examples of this invention,substantially the same mole percent (5.5) of MAC as p-cumyl phenylchloroformate was used. The table below compares the molar concentrationof DAC between the Bussink results and the process of this invention.The process of this invention has a significantly lower molar level ofDAC in the polycarbonate product than the lowest level reported byBussink et al.

MAC Addition Interval (% of Total Phosgene to Product DAC levelmicromole Process Polycarbonate Reactor) DAC/mole Repeat Unit Bussink etal  0 (single point) 388 ″ 20 (single point) 157 ″ 30 (single point) 128″ 40 (single point) 139 This Invention 10–40 Interval 42–124 (range ofDAC levels in Examples 10–11)

This invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

1. A continuous process for the preparation of monofunctional aromaticchloroformates (MAC) having the structure (I)

wherein n is an integer from 1 to 5, and R₁ represents hydrogen, abranched or unbranched alkyl group having from 1–15 carbon atoms, anaryl group which may be substituted or unsubstituted, a cycloaliphaticgroup which may be substituted or unsubstituted, or an arylalkyl groupwhich may be substituted or unsubstituted, the method comprising thesteps of a) introducing 1) an aqueous caustic solution; 2) a carbonylchloride; 3) at least one monofunctional hydroxyaromatic compound; and4) at least one inert organic solvent into a continuous reaction system;and b) effecting contact between 1), 2), 3) and 4) for a time and atconditions sufficient to produce a MAC of structure (I).
 2. The methodof claim 1, wherein the continuous process is effected in a tubularreactor having from one to four stages.
 3. The method of claim 1,wherein the continuous process is effected in a tubular reactor havingone stage.
 4. The method of claim 1, wherein the continuous reactionsystem contains less than 50 ppm of triethylamine.
 5. The method ofclaim 1, wherein in the continuous reaction system, the contact betweenthe aqueous caustic solution, the carbonyl chloride, the monofunctionalhydroxyaromatic compound and the inert organic solvent is conducted inthe absence of organo-phosphorous catalysts.
 6. The method of claim 1,wherein the monofunctional hydroxyaromatic compound is selected from thegroup consisting of phenol, p-tert-butylphenol, o-cresol, m-cresol,p-cresol, o-ethylphenol, p-ethylphenol, p-cumylphenol, chroman,p-octylphenol, p-nonylphenol, α-napthol, β-napthol and a mixturethereof.
 7. The method of claim 1, wherein the monofunctionalhydroxyaromatic compound is selected from the group consisting ofphenol, t-butyl phenol, p-cumyl phenol, chroman, and a mixture thereof.8. The method of claim 1, wherein the monofunctional hydroxyaromaticcompound is p-cumyl phenol.
 9. The method of claim 1, wherein thecontinuous process is operated as an on-demand process and is coupled toa batch polycarbonate synthesis.
 10. The method of claim 2, wherein theresidence time in the continuous reaction system is from about 0.5seconds to about 30 seconds per stage.
 11. The method of claim 2,wherein the residence time in the continuous reaction system is fromabout 0.5 to about 10 seconds per stage.
 12. The method of claim 3,wherein the residence time in the continuous reaction system is about0.5 seconds to about 30 seconds.
 13. The method of claim 3, wherein theresidence time in the continuous reaction system is from about 0.5 toabout 10 seconds.
 14. The method of claim 1, wherein the carbonylchloride and the monofunctional hydroxyaromatic compound are introducedinto the reaction system at a first molar flow rate ratio of from about1.05:1 to about 10:1; and the caustic and the monofunctionalhydroxyaromatic compound are introduced into the reaction system at asecond molar flow rate ratio of from about 1.1:1 to about 3:1.
 15. Themethod of claim 1, wherein the weight of the monofunctionalhydroxyaromatic compound relative to the weight of inert organic solventis from about 0.5:99.5 to about 20:80.
 16. The method of claim 1,wherein the strength of the aqueous caustic solution is about 10 toabout 50 weight percent.
 17. The method of claim 1, wherein the contentsof the reaction system are maintained at a temperature of below about60° C.
 18. The method of claim 1, wherein the carbonyl chloride isphosgene.
 19. The method of claim 1, wherein the inert organic solventis selected form the group consisting of pentane, hexane, cyclohexane,heptane; toluene, xylene; chlorobenzene, dichlorobenzene, nitrobenezene;chloroform; methylene chloride, and mixtures thereof.
 20. The method ofclaim 1, wherein the inert organic solvent is methylene chloride. 21.The method of claim 1, wherein steps a) and b) are conductedsimultaneously.
 22. The method of claim 1, wherein the process isoperated adiabatically.
 23. A continuous process for the preparation ofan MAC product having the structure (I)

wherein n is an integer from 1 to 5, and R₁ represents hydrogen, abranched or unbranched alkyl group having from 1–15 carbon atoms, anaryl group which may be substituted or unsubstituted, a cycloaliphaticgroup which may be substituted or unsubstituted, or an arylalkyl groupwhich may be substituted or unsubstituted, the method comprising thesteps of a) providing a reaction system comprising a reactor consistingessentially of a tubular reactor and a means for conveying fluidsthrough the reactor; the tubular reactor having an input at the upstreamend and an outlet at the downstream end; b) introducing into the tubularreactor at the input of the upstream end a feed stream comprising aninert organic solvent and a monofunctional hydroxyaromatic compound; c)introducing into the tubular reactor a carbonyl chloride; d) introducinginto the tubular reactor an aqueous caustic solution; e) effectingcontact between the carbonyl chloride, the monofunctionalhydroxyaromatic compound and the aqueous caustic solution for a timeperiod and at conditions sufficient to yield the MAC product.
 24. Themethod of claim 22, wherein the reaction system further comprises afirst precooler, a second precooler, and a mixer that is coupled withthe first precooler, wherein the monofunctional hydroxyaromatic compoundis dissolved in the inert organic solvent and fed to the first precoolerand upon exiting the first precooler is fed to the mixer, and whereinthe aqueous caustic solution is fed to the second precooler; the streamsexiting the first and second precoolers being fed to the tubularreactor.
 25. The method of claim 23, wherein the carbonyl chloride isintroduced at the upstream end of the tubular reactor.
 26. The method ofclaim 23, wherein the aqueous caustic solution is introduced at theupstream end of the tubular reactor.
 27. The method of claim 23, whereinthe carbonyl chloride is dissolved in the feed stream that is introducedat the upstream end of the tubular reactor.
 28. The method of claim 23,wherein the carbonyl chloride is phosgene.
 29. The method of claim 23,wherein steps b) through e) are conducted simultaneously.
 30. The methodof claim 23, wherein the carbonyl chloride and the monofunctionalhydroxyaromatic compound are introduced into the tubular reactor at afirst molar flow rate ratio of from about 1.05:1 to about 10:1; and thecaustic and the monofunctional hydroxyaromatic compound are introducedinto the tubular reactor at a second molar flow rate ratio of from about1.1:1 to about 3:1.
 31. The method of claim 23, wherein in the reactionsystem, the contact between the aqueous caustic solution, the carbonylchloride, the monofunctional hydroxyaromatic compound and the inertorganic solvent is conducted in the absence of additional catalysts. 32.The method of claim 23, wherein the continuous reaction system containsless than 50 ppm triethylamine.
 33. The method of claim 23, wherein inthe reaction system, the contact between the aqueous caustic solution,the carbonyl chloride, the monofunctional hydroxyaromatic compound andthe inert organic solvent is conducted in the absence oforgano-phosphorous catalysts.
 34. The method of claim 23, wherein theprocess is operated adiabatically.
 35. The method of claim 23, whereinthe process is operated in such a manner that the Reynolds number isfrom 200 to 100,000.
 36. A continuous process for the preparation ofparacumyl phenyl chloroformate comprising the steps of: a) providing areaction system comprising a reactor consisting essentially of a tubularreactor and a means for conveying fluids through the reactor; thetubular reactor having an input at the upstream end and an outlet at thedownstream end; b) introducing into the tubular reactor at the input ofthe upstream end a feed stream comprising methylene chloride andparacumyl phenol; c) introducing phosgene into the tubular reactor; d)introducing an aqueous caustic solution into the tubular reactor; e)effecting contact between the phosgene, the paracumyl phenol and theaqueous caustic solution for a time period and at conditions sufficientto yield paracumyl phenyl chloroformate.
 37. The method of claim 36,further comprising the step of f) recovering a product stream comprisingparacumyl phenyl chloroformate from the outlet end of the tubularreactor.
 38. A continuous process for the preparation of monofunctionalaromatic haloformate having the structure V

wherein n is an integer from 1 to 5, and R₁ represents hydrogen, abranched or unbranched alkyl group having from 1–15 carbon atoms, anaryl group which may be substituted or unsubstituted, a cycloaliphaticgroup which may be substituted or unsubstituted, or an arylalkyl groupwhich may be substituted or unsubstituted, and X represents bromine,fluorine, iodine or chlorine; the method comprising the steps of a)introducing 1) an aqueous caustic solution; 2) a carbonyl halide; 3) atleast one monofunctional hydroxyaromatic compound; and 4) at least oneinert organic solvent into a continuous reaction system; and b)effecting contact between 1), 2), 3) and 4) for a time and at conditionssufficient to produce a MAC of structure (I).